1256 GMT May 26, 2019
Many chemicals have been linked to early puberty in animal studies including phthalates, which are often found in scented products like perfumes, soaps and shampoos; parabens, which are used as preservatives in cosmetics; and phenols, which include triclosan, researchers note in Human Reproduction. While this is thought to interfere with sex hormones and puberty timing, few studies have explored this connection in human children, according to Reuters.
For the current study, researchers followed 338 children from birth through adolescence. They tested mothers' urine during pregnancy and interviewed them about potential chemical exposures, then tested kids' urine for chemical exposure at 9 years old and examined children for signs of puberty development every nine months between ages 9 and 13 years.
Over 90 percent of kids' urine samples showed concentrations of all the potentially hormone-altering chemicals, except for triclosan, which was found in 73 percent of pregnant mothers' urine samples and 69 percent of their kids' urine samples.
For every doubling in concentration of a phthalate indicator in mothers' urine, their daughters developed pubic hair an average of 1.3 months earlier, the study found. And with every doubling of mothers' urine concentrations of triclosan, girls started menstruating one month earlier.
Boys' puberty timing didn't appear to be influenced by prenatal exposure to these chemicals.
"There has been considerable concern about why girls are entering puberty earlier and hormone disrupting chemicals like the ones in personal care products that we studied have been suggested as one possible reason," said lead study author Kim Harley, associate director of the Center for Environmental Research and Children's Health at the University of California, Berkeley.
Half of the girls in the study started growing pubic hair when they were at least 9.2 years old and then began menstruating when they were 10.3 years old, the study found.
Phthalates, parabens and triclosan are not banned for use in personal care products, and there isn't solid evidence yet that they cause health effects in humans, Harley said by email.
But the current results add to increasing evidence from lab studies that suggests these chemicals can disrupt or interfere with natural hormones in the body like estrogen, Harley added.
"The fact that we find associations with earlier puberty in girls is additionally concerning," Harley said. "The good news is, that if women want to reduce their exposure to these chemicals, there are steps they can take."
Triclosan is no longer allowed in antibacterial soap in the US, but it is still in toothpaste, Harley said. Consumers should make sure it's not a listed ingredient on any toothpaste they buy, she advised.
Parabens are also on the ingredients list, often as methyl paraben, or propyl paraben, and consumers should avoid these products, too, Harley said.
Diethyl phthalate is harder to avoid, however, because it isn't listed on labels and is often used in fragrances, Harley said.